Pulse Code Modulation (PCM), as a traditional concept, means multiplexing voice service to E1/T1 by PCM. With its development, particularly for demand for data services, the PCM device is enhanced in its capability to support service. Now the concept of PCM is limited to multiplexing voice, but can handle multiple services such as voice, data, image, etc. to E1/T1 on the basis of time slot, as shown in FIG. 1. At the beginning, multiplexing of data and image services is realized through a V.35 interface, and the device only simply maps the V.35 channel to a time slot of E1/T1. It generally needs an outside protocol converter or Router for realizing the data service application with the V.35 interface. Nowadays, for more conveniently and simply realizing access of data services for users, PCM equipment can supply a 10M Ethernet interface to realize seamless access of user data.
PCM devices have been widely used in telecommunication and special networks, such as electric power, water conservancy and public security, because of its simple technology, flexible application and reasonable price. However, in networking applications with limited bandwidth, especially special networks, it is generally required to sufficiently utilize the trunk bandwidth because rental trunk bandwidth is limited. Particularly, when voice and data access are mixed, it is required that data services can occupy idle time slots while voice is not activated. However, service bandwidth is generally configured in a static state for a PCM device, and the bandwidth of data service is distributed to fixed time slots. Even if voice service is free, data service cannot occupy the idle bandwidth. If software is used to reconfigure the number of time slots for data service by detecting idle time slots, it will result in butting problems with opposing equipment and error codes in data services, and even service interruption caused by changing bandwidth.